Numerous contemporary medical procedures deliver drugs directly to target sites of diseased tissue. This targeted delivery has proven to be an advantageous approach for treating various medical conditions. Using targeted delivery, a controlled dose of the drug may be delivered directly to a target site while avoiding or minimizing exposing other parts of the body to the drug. Also, greater amounts of drug may be delivered to the afflicted parts of the body. In one approach to localized drug delivery, catheter-based, minimally invasive medical procedures are used for deploying devices such as stents, grafts, balloon catheters, and other intravascular devices.
One potential problem with these techniques is inadequate drug release (or inadequate control thereof) when the balloon is deployed. For example, in conventional drug eluting balloons, much of the drug can be lost due to washing away by the flow of blood as the balloon is being delivered to the target site.
In an effort to avoid these problems, certain drug eluting balloon systems include a sheath disposed around a balloon. One example, shown in FIGS. 5A and 5B, shows a sheath 110 provided around a balloon 120, with one or more holes 130 in sheath 110. As a gas or other working fluid is supplied through the device, balloon 120 expands. This expansion causes sheath 110 to expand as well, as shown in FIG. 5B. As sheath 110 expands, a drug provided within hole 130 is released to the target site.
These systems may have drawbacks, however. Although the shape of the hole stretches as the sheath expands, the hole itself remains relatively constant in volume. That is, the length (along the circumference of the sheath) increases as the depth of the hole decreases. As a result, less drug may be released during expansion. In some cases, as little as 10% of the drug may be released to the target site. To account for this, typical drug eluting balloons may need to include excess medicament in order to ensure that a target site receives the proper dose. In addition, these devices may have less-than-ideal control over the dosage of drug delivered to the target site.
Also, these systems may potentially lose medicament as the balloon moves through the vasculature to the target site. It can be difficult to predict the amount of medicament potentially lost as the device travels to a target site, which in turn makes it difficult to ensure that the proper amount of medicament actually reaches the target site.
Accordingly, there is a need for a drug eluting system that more effectively releases a medicament to a target site.